Chromium plating



CHROMIUM PLATING Paul J. Topelian, Newark, N. J., assignor to TiarcoCorporation, Newark, N. J., a corporation of New Jersey No Drawing.Application November 1, 1955 Serial No. 544,347

18 Claims. (Cl. 204-29) The invention relates to chromium plating and ismore particularly concerned with improved methods of depositing chromiumupon a chromium surface.

There are various instances where it is desired to deposit chromium uponan article which has been previously plated with chromium. Manyindustrial applications require articles plated with hard and densechromium of substantial thickness. Existing methods of depositing hardchromium from chromic acid plating baths, however, do not permitdeposition of more than a few thousandths in thickness before thedeposit begins to show signs of cracking. Continued plating results inpaths or openings in the chromium surface layer which lead to theunderlying or base metal. Where the underlying metal is not corrosionresistant, a chromium layer having such openings therein does not impartthe desired corrosion resistance to the article. If, before unduecracking occurs, the deposition of chromium can be interrupted and theplated article subsequently plated with an additional layer of chromium,the fresh or additional deposit will cover cracks or incipient cracks inthe initial deposit, and thereby furnish increased resistance tocorrosion. Whatever lines of cracking may appear in the overlyingchromium deposit generally are not in alignment with cracks or openingsin the initial chromium deposit.

It is frequently desirable to deposit chromium upon an object to veryclose dimensional tolerances. However, if upon removal from the chromiumplating bath, the article is undersize, then it becomes necessary todeposit an additional thickness of chromium on the chromium platedsurface. If the thickness of chromiumis over-size, the excess amount canbe buffed or ground off if the characteristics of the chromium surfacelayer and its adherence to the initially deposited chromium are such asto permit such subsequent operations.

Where the surface layer of a chromium plated article has become worn, itis highly desirable to deposit a fresh coating of chromium directly onthe article without resorting to the painstaking, costly and diflicultto control procedure of stripping the initial chromium deposit.

In each of the foregoing instances involving the deposition of chromiumupon a previously chromium plated surface, the chromium surface layermust be strongly adherent, particularly if the rigid requirements ofvarious industrial applications are to be met.

Prior to my invention, great difficulties have been encountered inendeavors to satisfactorily deposit chromium upon an object or articlewhich had been previously plated with chromium. The solid surfacestructure of the initial chromium deposit does not accept the new oradditional chromium deposit. A zone of weakness or line of cleavageoccurs between the initial and subsequent chromium deposits so thatadequate adhesion of the new deposit has been diflicult to obtain.Moreover, where, it has been desired to deposit chromium upon a wornchromium surface, the metals underlying the worn chromium surface havefurther complicated the problem. Any preliminary or conditioningtreatment designed to make the worn atent 2,856,334 Patented Oct. 14,1958 chromium receptive to the deposition of an additional thickness ofchromium must be of a nature and character which will not adverselyaffect, or be unduly reactive with, the metal in the areas beneath theworn or unduly thin chromium. In addition, the chromium deposit must notonly be tightly adherent to the underlying chromium, it must also bestrongly adherent to the metal other than chromium at areas which may beworn.

One of the primary objects of the present invention is to simply andeffectively treat or condition an object having a chromium surface topermit direct plating thereof with,

chromium to provide a strongly adherent deposit.

Another object of the invention is to prepare a previously platedchromium surface for the deposition of a strongly adherent layer ofchromium in a manner which permits the utilization of standard or commonhard chromium plating baths under normal or ordinary plating conditionsin a minimum amount of time.

Still another object of the invention is to provide a conditioningtreatment for the strong adhesion of a chromium deposit to a chromiumsurface which permits wide latitude in time of treatment, therebyeliminating exacting and costly procedural controls.

Still a further object of the invention resides in depositing chromiumdirectly upon a worm chromium surface to provide a strong bond with theunderlying chromium which may be exposed at the worn or thin chromiumcoated areas.

These, and other objects and advantages of the invention will beapparent from the following and more detailed description.

I have found that articles having a chromium surface or a chromium platethereon may be simply and effectively prepared for direct plating withchromium by subjecting the articles to the action of hydrogen chloridein the form of the gas, vapor or fumes. After chromium plating, thedeposited metal is strongly adherent and will Withstand severemechanical abrasion and distortion en-v piped into the chamber in whichthe article is suspended.

for treatment. It is preferred, however, to provide the hydrogenchloride gas, vapor or fumes by heating or boiling hydrochloric acid inthe same chamber or vessel in which the article is suspended to receivethe conditioning treatment. The acid may be fully concentrated ordiluted,

and commercial muriatic acid having a concentration of 18 B. willfurnish satisfactory results. Whatever concentration of acid is used,upon heating the acid under atmosphericconditions, the concentration ofthe acid soon reaches a point of stabilization or equilbiriurn where theconcentration of the acid is approximately 20.4%. A gas temperature atapproximately F. to F. in the vicinity of the article is preferred. Ifthe article being conditioned has a worn chromium surface coating whichexposes an underlying metal such as zinc, lead, or aluminum, care shouldbe exercised to prevent the article from coming in direct contact withthe heated acid.

Describing the invention in greater detail, the chromium surfacedarticle to be conditioned and plated with chromium is first cleaned inany suitable manner as by immersion in a hot caustic soda bath or byliquid honing (a pressure blast of chemical emulsion and fine abrasivein solution). The article is then suspended in a chamber or vessel andsubjected to the action of the hydrogen chloride gas formed by heatinghydrochloric acid in the same chamber until the chromium surface shows agreen color. The time of treatment depends upon the temperature of thegas in the vicinity of the article, the surface area of the article andthe rate of flow of the gas over the surface to be conditioned. A gastemperature of approximately 140 F. to 170 F. in the vicinity of thearticle has been found to furnish satisfactory results. The time oftreatment may vary from just a few seconds to several minutes, and isnot critical. There are no adverse effects if the article is subjectedto activation for an extended period of time. In any event, activationis indicated as completed when the chromium assumes the aforementionedgreen color. The article is then removed from the gaseous medium, givena thorough rinse in cold Water, which preferably is followed byimmersion in a hot aqueous chromic acid solution. This solutionpreferably contains 28 ounces per gallon of chromic acid maintained at atemperature of approximately 175 F. The time of immersion in the'hotchromic acid solution is approximately one minute. Then, without furtherrinsing, the article is made the cathode in a chromium plating bath.

Any'commercial chromium plating bath maybe used to deposit chromium uponthe article conditioned in the manner above described. A chromiumplating bath which has been found particularly suitable for thedeposition of hard, dense or industrial chromium contains 33 ounces pergallon of chromic acid and 0.33 ounce per gallon of sulphate in the formof sulphuric acid. The bath is maintained at a temperature ofapproximately 132 F., and a current density of approximately 3 amperesper square inch is used. The bath composition and condi tions describedwill provide a chromium deposit of 0.001 inch per hour. Plating may beextended for as long as 20 hours, and'the plate is strongly adherent.

Another bath which has provided hard, dense and tightly adherentchromium deposits upon a chromium surfaced article aftercon'ditioning inthe manner above described is a 'bath'containing '54 ounces per gallonof chromic acid and 0.54 ounce per gallon of sulphate in the form ofsulphuric acid. With a bath of this composition, a'temperature ofapproximately 122 F. is main tained with a current density ofapproximately 1.5 amperes per square inch. The bath composition andplating conditions described will furnish "0.0005 inch of deposit perhour. I

The metal-underlying the initial chromium deposit may be ferrous,aluminum, zinc, lead,'titanium, copper, nickel. Ferrous, aluminum, zinc,lead, titanium, copper, and nickel as used in the claims are intended ina generic sense to include both a commercially pure metal and alloysofthe metal which are predominantly, or contain a substantial amount of,iron, aluminum, zinc, lead, titanium, copper and nickel, respectively.Even if portions of the chromium are worn, and areas of the base metalare partially exposed, or covered with only a very thin coatingofchromium, the hydrogen chloride gas treatment to activate the articlefor the subsequent deposition of chromium does not deleteriously affectthe base or underlying metal. In fact, the underlying or base metal isalso activated to permit excellent bonding with a subsequent chromiumdeposit.

While as previously stated, the chromium plated article may be given asuitable cleaning prior to the hydrogen chloride gas treatment, I havefound that the gas treatment possesses a cleaning function in additionto its function of makin the chromium surface receptive to subsequentplating with chromium-with strong adherence. The same is true where theinitial chromium deposit is worn and another metal is exposed in spots.Thus, it is .within the scope of the invention to eliminate preliminarycleaning operations prior to treatment with the hydrogen chloride gas.

It will be apparent that the deposition of chromium on a worn chromiumsurface involves deposition upon a surface which is not linearly smooth,and therefore may result in a final chromium deposit which may requirebufling or grinding. The chromium deposited upon an article conditionedin the manner above described is so tightly adherent that the mechanicalabrasion incident to grinding will not result in chipping, peeling orflaking of the chromium. Such subsequent operation is much less costlyand laborious than is involved in a stripping procedure.

In lieu of the hydrogen chloride gas, hydrogen bromine, hydrogenfluorine, or hydrogen iodine gas, vapor or fumes may be used. Hydrogenchloride gas, however, is preferred, because of the advantages of costand handling.

It is believed that the novel process of the present invention, as wellas the advantages thereof, will be apparent from the foregoing detaileddescription. It also will be apparent that While the invention has beendescribed in its preferred form, changes may be made without departingfrom the spirit and scope of the invention as sought to be defined inthe following claims.

I claim:

1. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment with ahydrogen halide gas, removing the article from the gaseous medium whenthe chromium surface assumes a green color, and electroplating chromiumon the chromium surface of the article.

2. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment with aheated hydrogen halide gas, removing the article from the gaseous mediumwhen the chromium surface assumes a green color, and electroplatingchromium on the chromium surface of the article.

3. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment with aheated'hydro'gen' halide gas, the temperature of the gas-in the vicinityof the article beingapproximately F. to F.,.removing the article fromthe gaseous medium when the chromium surface assumes a green color, andelectroplating chromium on the chromium surface of the article.

4. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment with aheated hydrogen halide gas, said gas being formed by heating "a hydrogenhalide solution in the same chamber in which the article is suspendedfor treatment, the temperature of the gas in the vicinity of the articlebeing approximately 140 F. to 170 F., removing the article from'thegaseous medium when the chromium surface assumes a green color, andelectroplating chromium on the chromium surface of the article.

5. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment with aheated hydrogen halide gas, removing the article from the gaseous mediumwhen the chromium surface assumes a green color, rinsing the article inwater, immersing the article in a heated aqueous chromic acid solution,making the article a cathode in a chromium plating bath, andelectroplating chromium on the chromium surface of the article.

6. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment withhydrogen chloride gas, removing the article from the gaseous medium whenthe chromium surface assumes a green color, and electroplating chromiumon the chromium surface of the article.

7. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment withheated hydrogen chloride gas, removing the article from the gaseousmedium when the chromium surface assumes a green color, andelectroplating chromium on the chromium surface of the article.

8. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment withheated hydrogen chloride gas, the temperature of the gas in the vicinityof the article being approximately 140 F. to 170 F., removing thearticle from the gaseous medium when the chromium surface assumes agreen color, and electroplating chromium on the chromium surface of thearticle.

9. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment withheated hydrogen chloride gas, said gas being formed by heatinghydrochloric acid in the same chamber in which the article is suspendedfor treatment, the temperature of the gas in the vicinity of the articlebeing approximately 140 F. to 170 F., removing the article from thegaseous medium when the chromium surface assumes a green color, andelectroplating chromium on the chromium surface of the article.

10. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting Said surface to a treatment withheated hydrogen chloride gas, removing the article from the gaseousmedium when the chromium surface assumes a green color, rinsing thearticle in water, immersing the article in a heated aqueous chromic acidsolution, making the article a cathode in a chromium plating bath, andelectro plating chromium on the chromium surface of the article.

11. A process of chromium electroplating an article having a chromiumplated surface comprising subjecting said surface to a treatment withheated hydrogen chloride gas, the temperature of the gas in the vicinityof the article being approximately 140 F. to 170 F., said gas beingformed by heating hydrochloric acid in the same chamber in which thearticle is suspended for treatment, removing the article from thegaseous medium when the chromium surface assumes a green color, mak ingthe article a cathode in a chromic acid plating bath comprising 33ounces per gallon of chromic acid and 0.33 ounce per gallon of sulphate,and plating the article at a current density of approximately 3 amperesper square inch with the temperature of the bath at approximately 132 F.

12. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith a hydrogen halide gas, removing the article from the gaseous mediumwhen the chromium surface assumes a green color, and electroplatingchromium on said worn chromium surface and underneath metal of thearticle.

13. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith a heated hydrogen halide gas, removing the article from the gaseousmedium when the chro mium surface assumes a green color, andelectroplating chromium on said worn chromium surface and underneathmetal of the article.

14. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith hydrogen chloride gas, removing mium surface assume a green color,and electroplating chromium on said worn chromium surface and underneathmetal of the article.

15. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium copper, andnickel, said process comprising subjecting said surface to a treatmentwith heated hydrogen chloride gas, removing the article from the gaseousmedium when the chromium surface assumes a green color, andelectroplating chromium on said worn chromium surface and underneathmetal of the article.

16. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith heated hydrogen chloride gas, the temperature of the gas in thevicinity of the article being approximately F. to F., removing thearticle from the gaseous medium when the chromium surface assumes agreen color, and electroplating chromium on said worn chromium surfaceand underneath metal of the article.

17. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith heated hydrogen chloride gas, said gas being formed by heatinghydrochloric acid in the same chamber in which the article is suspendedfor treatment, removing the article from the gaseous medium when thechromium surface assumes a green color, and electroplating chromium onsaid worn chromium surface and underneath metal of the article.

18. A process of chromium electroplating an article having a wornchromium plated surface which exposes the underneath metal, the metalbeneath said worn chromium surface being selected from the groupconsisting of ferrous, aluminum, zinc, lead, titanium, copper, andnickel, said process comprising subjecting said surface to a treatmentwith heated hydrogen chloride gas, removing the article from the gaseousmedium when the chromium surface assumes a green color, rinsing thearticle in water, immersing the article in a heated aqueous chromic acidsolution, making the article a cathode in a chromium plating bath, andelectroplating chromium on said worn chromium surface and underneathmetal of the article.

References Cited in the file of this patent UNITED STATES PATENTS1,608,694 Cain Nov. 30, 1926 1,774,901 Piersol Sept. 2, 1930 2,028,312Bornhauser Jan. 21, 1936 2,091,386 Viers Aug. 31, 1937 2,096,434 LukensOct. 19, 1937 2,285,549 Wesley et al. June 9, 1942 2,293,810 Domm Aug.25, 1942 2,574,305 Wagner Nov. 6, 1951 2,728,719 Tucker et al. Dec. 27,1955 FOREIGN PATENTS 503,008 Great Britain Mar. 29, 1939 OTHERREFERENCES Metal Industry, May 12, 1944, pages 299-300, Chrothe articlefrom the gaseous medium when the chro- 75 mium Plating on Steel.

1. A PROCESS OF CHROMIUN ELECTROPLATING AN ARTICLE HAVING A CHROMIUMPLATED SURFACE COMPRISING SUBJECTING SAID SURFACE TO A TREATMENT WITH AHYDROCARBON HALIDE GAS, REMOVING THE ARTICLE FROM THE GASEOUS MEDIUMWHEN THE CHROMIUM SURFACE ASSUMES A GREEN COLOR, ANDD ELECTROPLATINGCHROMIUM ON THE CHROMIUM SURFACE OF THE ARTICLE.